Monday, December 07, 2015

Turned out Wet (again)

[Update 26th December 2015: It's still raining. Much of northern England has had its wettest December on record. UK Government still in material denial over significant action on global warming.]In February 2014, at the time of the Somerset Levels flooding, I wrote a couple of blog-pieces about the weather (well, I am English). They are here: Turned out Wet and here:Turned out Wet (and still raining)In case you don't want to follow those links I'll repost the first section, which turns out still to be relevant:

Climate scientists talk of extreme weather in terms of 3-sigma or even 5-sigma events. In a distribution of possibilities 3-sigma refers to the probability of something happening that lies at least 3 standard deviations away from the norm. For a normal distribution that’s a chance of some 1 in 370. A 5-sigma event has a probability of about 1 in 1.7 million, so you really should not be holding your breath waiting for it to happen.

The real world is not quite so simple. The probabilities of weather events are not distributed evenly about the mean – a dry day can’t get any drier but a wet day could be a lot wetter. Skewed or fat-tailed distributions are common. But to get a qualitative handle on things for practical purposes, such as whether it’s worth spending money on a particular flood defence, one might consider a 3-sigma event as very rare, maybe having occurred during the historical record just once or twice or not at all. That’s the sort of probability that the Environment Agency seriously considers planning for and often spends big money on defending against. There will always be some who say the money should not be spent, or should be spent differently, but that’s all part of the normal cut and thrust of public policy making and spending.

A 5-sigma event, even with fat-tailed weather event distributions, is so rare it’s probably never been experienced and may never have happened at least during much of the last few thousand years of the Holocene climate regime. Most people in a democracy would baulk at policies and public spending to protect against 5-sigma events. And if there are downsides to a policy that protects against such an event then it is soon and sensibly ruled out.

However, such thinking presupposes that the climate is stable, that what were 3-sigma events haven’t become a whole lot more common and that the previously 5-sigma events have not now slipped into the 3-sigma category. But that is exactly what climate science tells us to expect in a warming planet. The global warming caused by our emission of carbon dioxide and other greenhouse gasses is producing climate changes that are shifting the probabilities. For the British Isles more stormy weather with higher rainfall totals falling with greater intensity, interspersed with occasional severe droughts, is the future we need to expect.

The winter of 2013/4 has seen a 5-sigma event in southern Britain. Rainfall has been the highest in the record and the number, frequency and intensity of Atlantic depressions has surpassed previous knowledge. One might justifiably wonder whether there has been a similar period of stormy weather since the Atlantic Period, since the Neolithic settlers built the Sweet Track across the Somerset Levels.

Ian Liddell-Grainger, MP for Bridgwater and West Somerset, asked, rhetorically, “Was it climate change or incompetence?” and stated, “These floods were predictable”. His opposition to windfarms and poor voting record in Parliament on climate related issues, makes one think that here is a man who does not understand climate science and does not take climate change seriously. But then he is a parliamentarian who, presumably, feels the need to represent the views of his constituents. Opinion surveys have shown that a large proportion of the British public do not accept the scientific consensus on climate change, so perhaps Mr Liddell-Grainger is not unusual.

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Almost two years on and in the light of the rainy weather in Cumbria and elsewhere it's time to re-visit the issue. We've just seen another extreme rainfall event; the Honister weather station recorded 341mm in 24 hours, a new UK record. That's certainly a 3-sigma event, maybe a 5-sigma, but that depends on how one does the statistics. As I suggested in February 1014 (copied above) we should be looking at the dynamic aspect of the weather record; the climate is no longer stable so that which should once have been regarded as so unlikely it can, for practical and policy purposes be regarded as 'won't happen' should now be expected, mitigated against and adapted to.This is where the weather buffets politics. Last time I took a passing swipe at the Somerset MP, Ian Liddell-Graingers's grasp of climate science so let's now, in fairness, turn to the Penrith MP, Rory Stewart. What's his Parliamentary record on climate change?

Climate Change: There have been votes in Parliament on targets for reducing carbon dioxide emissions and on increasing the proportion of electricity generated via renewable means as well as on the establishment of a UK Green Investment Bank, to invest in projects which, for example, reduce greenhouse gas emissions.

Rory Stewart generally voted against measures to prevent climate changeStewart is not just the local MP, he is Parliamentary Under Secretary of State at the Department for Environment, Food & Rural Affairs (DEFRA), so he was being interviewed for the television news in wellies and hi-viz in front of a flooded street scene. To his credit, though I don't suppose he realised it, he got it right when he suggested that talking in terms of a one in hundred year event is not helpful. I think, however, he meant helpful as in helping the damp folks piling their carpets on the street, rather than the statistical meaninglessness of 'one in a hundred years' when the climate is changing.

It was only four weeks ago that an up-beat Rory Stewart said: “This is a real model of local river management" while on a visit to a flood management project in his constituency. Stewart, as befits the 'Floods Minister', has actually involved himself and written quite a lot on the flooding issue, as can be seen from his own blog. It's good to see, and perhaps surprising from a man more well-known for his writings about walking in the deserts of central Asia.

But, and please help me if I've missed it, he appears to have not noticed the elephant in the room. He never mentions global warming. Sorry, Rory, but it's well past time to push your government into serious global warming mitigation and adaptation instead of allowing the UK to be seen in Paris COP21 as the world's laggards.

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